The present invention relates to a copier, printer, facsimile apparatus or similar electrophotographic image forming apparatus. More particularly, the present invention relates to an image forming apparatus of the type including a rotary unit rotatable relative to an apparatus body and a drive unit for causing the rotary unit to rotate to and stop at a preselected position.
Today, a color image forming apparatus of the type including a revolver type developing unit, which is a specific form of a rotary unit, is extensively used. To enhance high-speed operation and high durability, it is necessary with the apparatus of the type described to reduce a color switching time, i.e., to rotate the revolver at high speed. It is also necessary to provide the revolver with rigidity high enough to withstand sharp drive and stop and to guarantee an accurate development gap. Further, the diameter of a developing roller must be increased to cope with high linear velocity for development. In addition, the amount of developer must be increased in order to extend a maintenance period. However, higher rigidity, larger roller diameter and greater amount of developer increase the size and weight of the revolver. This results in the need for a revolver drive motor having power great enough to drive the revolver increased in the moment of inertia at high speed.
The great power, revolver drive motor must be accompanied by a sufficient measure against vibration. The vibration of the motor effects, e.g., writing accuracy and thereby brings about jitter images when transferred to the apparatus body. In addition, the vibration turns out high-frequency noise that annoys the operator of the apparatus. It is a common practice to position a motor mount or vibration preventing member, which includes a rubber member, between the apparatus body and a motor mounting surface for thereby intercepting the vibration of the motor. The motor mount may be implemented by, e.g., a pair of metal plates adhered to opposite sides of a rubber member. However, it was experimentally found that such a motor mount broke due to aging when applied to a drive unit for driving the revolver. Not only the revolver but also other rotary units suffer from such damage.
Japanese patent laid-open publication No. 11-035091, for example, discloses an image forming apparatus including a vibration preventing member and a motor position restricting member. The vibration preventing member intervenes between a motor case mounting surface substantially perpendicular to the axis of a motor member. The motor position restricting member contacts or adjoins a motor case surface substantially parallel to the axis of the motor member. The apparatus taught in the above document is constructed to shut off vibration and noise ascribable to a motor member that drives a driven gear mounted on a rotary unit via a drive gear. The motor position restricting member is configured to prevent the motor member from shaking due to a reaction exerted by the driven gear when the rotary unit is in rotation.
The prior art apparatus described above, however, has the following problem left unsolved. The motor position restricting member supports the motor case of the motor member in such a manner as to prevent it from being displaced. As a result, vibration ascribable to motor rotation is transferred to the apparatus body via the motor position restricting member. Particularly, in a high speed, color image forming apparatus, the motor position restricting member transfers, depending on its position, motor vibration to the apparatus body at such a timing that motor rotation and the writing of a latent image on an image carrier overlap. This degrades image quality to a critical degree.
Technologies relating to the present invention are also disclosed in, e.g., Japanese patent laid-open publication Nos. 11-295961 and 2000-235292.
It is therefore an object of the present invention to provide an image forming apparatus capable of enhancing the durability of a vibration preventing member against aging and protecting a rotary unit from defective rotation ascribable to damage to the vibration preventing member to thereby insure stable images.
In accordance with the present invention, an image forming apparatus includes an apparatus body and a rotary unit rotatable relative to the apparatus body. A drive unit causes the rotary unit to rotate to and stop at a preselected position. The drive unit includes a motor member and a vibration preventing member intervening between the motor case mounting surface of the motor member, which is substantially perpendicular to the axis of the motor member, and the apparatus body. The motor member is mounted on the vibration preventing member. A motor support member supports the weight of the motor member on a motor case surface substantially parallel to the axis of the motor member.
Also, in accordance with the present invention, an image forming apparatus includes an apparatus body and an image carrier for forming a latent image thereon. A writing unit writes the latent image on the image carrier. A rotary unit is rotatable relative to the apparatus body. A drive unit causes the rotary unit to rotate to and stop at a preselected position. The drive unit includes a motor member and a vibration preventing member intervening between the motor case mounting surface of the motor member, which is substantially perpendicular to the axis of the motor member, and the apparatus body. The motor member is mounted on the vibration preventing member. A motor position restricting member contacts or adjoins a motor case surface substantially parallel to the axis of the motor member. The motor position restricting member is so positioned as to obstruct the displacement of a motor case ascribable to a force exerted by the rotary unit on the motor member when the drive unit is driving the rotary unit, but when the writing unit does not write a latent image on the image carrier.